1. Field of the Invention
This invention relates to a small brush motor and in particular to a structure of a rotator containing an armature and a commutator unit.
2. Related Art
A rotator 100 in a small brush motor of a general 2-3 (2-magnetic-pole-3-salient-pole) structure shown in FIG. 9 comprises an armature core 101 with coil windings 110 different in phase wound around three salient poles 102, a commutator unit 106 having three commutator pieces 103 separated by a slit 104, and a shaft 105 onto which the armature core 101 and the commutator unit 106 are fitted. The energization change timing accuracy of the small brush motor for the coil winding 110 of each phase is affected mainly by the alignment accuracy between a center line P1 of the salient pole 102 and a center line P2 of the slit 104. Therefore, if the center lines P1 and P2 are out of alignment in the circumferential direction, the energization change timing accuracy for the coil windings 110 worsens, resulting in an increase in cogging and torque ripple.
Then, formerly, when the commutator unit 106 was pressed into the shaft 105, a jig, etc., was used for performing rough positioning.
In the small brush motor, a slight space S in a thrust direction is provided between the rotator 100 and a motor case 107. As shown in FIG. 10, the dimensions between the space S are adjusted according to the dimensions of the inner bottom face of the motor case 107 and the projection of an insulator 108 of the armature core 101, or the thickness of an adjustment plate 109 sandwiched between one end part of the shaft 105 and the motor case 107.
Further, to wind the coil winding 110 around the salient pole 102 of the armature core 101, an annular base 110 for joining the salient poles 102 is not provided with a member for supporting a winding end part 112 of the coil winding 110. If free winding is executed with a coil winder, the coil winding 110 may be shifted into the base 111, causing winding break.
Moreover, as shown in FIG. 11, a collar 117 of a commutator holder 115 is molded thin and if the press force of a soldering iron 114 is too large or the crimping time of the soldering iron 114 is too long in soldering work for electrically connecting the coil winding 110 to a riser 113, the riser 113 is bent in the arrow B direction or if the commutator holder 115 is made of a synthetic resin, heat deformation H is easily caused.
As described above, in the small brush motor of a general 2-3 (2-magnetic-pole-3-salient-pole) structure, an effect can be produced by rough positioning with a jig, etc., when the commutator unit 106 is pressed into the shaft. However, with a small brush motor of a 4-6 (4-magnetic-pole-6-salient-pole) structure with a larger number of salient poles, the numbers of slits 104 and commutator pieces 103 are increased, thus the open angle of each commutator piece becomes a half or less and the contact area with the commutator holder 115 is decreased. Resultantly, the commutator pieces 103 easily fall down and the assembly accuracy of the commutator unit 106 and the position accuracy between the salient poles 102 of the armature core 101 and the commutator unit 106 are required to be stricter.
In the space S adjustment method in the related art, variations occur in a cumulative error of each dimension accuracy of the dimensions of pressing the armature core 101 into the shaft 105, the thickness of the armature core 101, the thickness of the insulator 108, and the thickness of the adjustment plate 109, thus it becomes difficult to provide accuracy. The effect largely appears particularly when the motor is flattened.
Further, for the winding break of the winding end part 112 in the base 111, the small brush motor of 2-3 structure, which has a small number of salient poles, is easily adjusted in a wide work space; with the small brush motor of 4-6 structure, the spacing between the salient poles becomes narrow and it becomes difficult to correct the winding break, thus the winding cannot be thickened and the motor characteristics may be adversely affected.
Moreover, the small brush motor of 4-6 structure is crowded with a large number of soldering work points for the riser 113 as compared with the small brush motor of 2-3 structure, thus is easily filled with the soldering heat and moreover the portion of the commutator holder 115 holing the riser 113 is thin. Thus, the commutator unit 106 easily undergoes heat deformation, it becomes difficult to maintain accuracy, and the motor characteristics cannot be held uniform.